1. Field of the Invention
The present invention relates to a power control unit for an electronic device, and more particularly to the power control unit which may apply to a pair of electronic devices connected through a communication cable, one electronic device may control the power of the other electronic device.
2. Description of the Related Art
To control the power on or off of one device from the other device if two devices having the corresponding power sources are connected through a cable, the inventors of the present application know that there have been already proposed two techniques, which will be described below.
(1) In such a case that a power of the CRT is controlled from a personal computer.
Consider that a pair of electronic devices serving as a power feeder and a power receiver and the electronic device serving as the power feeder (controlling device) provides a plug socket, a power supply circuit, a power control circuit for the power supply circuit and the electronic device serving as the power receiver (controlled device) provides a power circuit and an AC cord with a plug. The plug of the controlled device is connected to the plug socket. When the controlled device is powered on, the power is fed to the plug socket from which the power is sent to the power supply circuit through the AC cord in the controlled device. In this arrangement, the controlled device is powered on or off by the controlling device.
(2) In such a case that the TV is powered on and off by remote control
The controlled device receives a command by any communication means from the controlling device and operates in response to this command. The communication means provides power on and off commands on which the controlled device is operated. To turn on the power supply circuit, it is necessary to constantly keep power on in the section for receiving the commands of the controlled device so that the section may receive the powered-on command from the controlling device for turning on the overall controlled device.
Next, consider that a portable electronic device such as an electronic note or a function calculator serves as controlling a power of its peripheral device.
The foregoing technique (1) is suitable to only the arrangement that both of the portable electronic device and the relevant peripheral device are AC powered and are located within the reach of the power cord. If any one of them is battery powered, it is necessary to connect both of them through a cable and transmit the voltage indicating a power on or off state from the controlling device to the controlled device. To do so, an extra cable and an extra terminal are required. So, the implementation of this arrangement needs to be costly.
To use the foregoing technique (2), it is necessary to constantly have power on the section for receiving a command, since the power on command has to be received while the controlled device is powered off. This is meaningful in the case that the power consumption of the section for receiving a command is far smaller than the overall circuit, such as in a TV.
However, the technique (2) is not meaningless in such a circuit arrangement like an electronic note that the section for receiving a command (normally configured of a communication interface, a CPU, a ROM, and a RAM, etc.) is considerably larger than the overall circuit arrangement. This is because the section cannot be operated while the power is turned off.
That is, in the small electronic device and its relevant peripheral device, the peripheral device is turned on immediately when the small electronic note served as the controlling device is turned on and the former is turned off when the latter is turned off. This operation is usually convenient. However, as mentioned above, as far as the inventors of the present applicant know, such a power control as the above is not applied to this arrangement. The power switches are normally provided in both of the small electronic device and the peripheral device.